LightSquared Claims Fix Will Cut 99% of Interference

One solution to this problem is to move the transmitted signal farther away
from the receiver being protected and another is to lower the power of the
interfering transmitter. LightSquared is proposing to take both of these
actions.
But will it work? Right now, nobody knows for sure. LightSquared is
convinced that it can eliminate interference to 99 percent of all GPS
receivers. That still leaves a lot of GPS receivers that will be affected, and
most of those appear to be high-precision devices used in science, surveying
and agriculture.

The U.S. GPS Industry Council argues otherwise, saying in their report that
LightSquared should not be permitted to use the L-band spectrum for their data
network. But their conclusion is based on the findings of the Technical Working
Group, which basically said the same thing.

The Industry Council refers to problems in limited testing of the lower 10MHz
portion of the L-band granted to LightSquared. The group said that 20 of 29
devices tested displayed "harmful interference." The group doesn't define what
harmful interference means in this case.
Where that leaves us is that LightSquared thinks its solution will work,
while the people backing the industry groups think it won't. Right now, nobody
knows for sure who is right. Clearly there needs to be more testing, and
LightSquared has already said it will hold off on deploying its system until
it's clear that there will be no interference.
Fortunately, the FCC doesn't have to make a decision on this until testing
of LightSquared's final system shows that it doesn't interfere with GPS. How
difficult that will be for LightSquared remains to be seen.

But in the meantime, there remain other options that might help. For
example, LightSquared's transmitters operate at 1,500 watts. Do they need to
use this much power? Cell towers, by comparison, average about 100 watts each
and manage to reach their customers with voice and data service.
Can LightSquared crank down the power knob and still work? Again, we don't
know because no tests have been run. Can LightSquared move to a different
frequency that's not next to GPS? Again, we don't know, but the L-band was originally
intended for satellite use, rather than terrestrial use, and that's part of the
problem.
So right now the answer is that there is no answer, and there won't be until
more testing is conducted.

Wayne Rash is a Senior Analyst for eWEEK Labs and runs the magazineÃÃÃs Washington Bureau. Prior to joining eWEEK as a Senior Writer on wireless technology, he was a Senior Contributing Editor and previously a Senior Analyst in the InfoWorld Test Center. He was also a reviewer for Federal Computer Week and Information Security Magazine. Previously, he ran the reviews and events departments at CMP's InternetWeek.

He is a retired naval officer, a former principal at American Management Systems and a long-time columnist for Byte Magazine. He is a regular contributor to Plane & Pilot Magazine and The Washington Post.